Choke valve especially used in oil and gas wells

Abstract

A choke valve specially used for regulating the flow volume and with it the back pressure of liquids or gas while drilling through shallow gas bearing formations from an off-shore drilling platform. The valve comprises a flexible cylindrical valve element (8) positioned in the valve housing (1) flow passage and where the valve is so designed that the valve element's (8) flow area can be reduced by a radial reduction of the valve element. The flow area of the valve element (8) is equal to or larger than the remaining flow area of the valve. The valve has devices (10;22) for constricting the end of the valve element (8) being nearest to the outlet opening (3) of the valve. The valve element (8) is so long that it is possible to compensate for the wear to which the end is exposed by sliding the valve element against the constricting devices (10:22) or by moving the latter along the valve element as the wear proceeds. Only the valve element (8) is exposed to wear and no other parts of the valve being positioned within the wearing zone. The valve element (8) in its withdrawn position has its total diameter free allowing a full flow through the valve. Accordingly the valve do not disturb the flow under normal condition and is not exposed to any wear. At a gas kick the well can be controlled during a long period as it is possible to compensate the wear on the valve element during operation.

I claim: 
     
       1. A choke valve comprising: an inlet at an upstream end thereof;   an outlet at a downstream end thereof;   a flexible tubular element between said inlet and said outlet;   a central passage in said flexible tubular element for permitting a flow of a fluid from said inlet to said outlet;   means for deforming a downstream end of said flexible tubular element into a controllable position selectively constricting said central passage; and   said means for deforming further including means for successively deforming additional portions of said flexible tubular element into said controllable position as deformed portions at said downstream end of said flexible tubular member are abraded away by said flow of a fluid, whereby an operating lifetime of said choke valve can be made as long as desired by increasing a length of said flexible tubular element and an operational range of said means for deforming.   
     
     
       2. A choke valve according to claim 1 wherein said central passage includes a diameter substantially equal to a diameter of said inlet and said outlet, when said flexible tubular member is in an undeformed condition. 
     
     
       3. A choke valve according to claim 1 wherein said means for deforming includes: an annular support adjacent said inlet;   an upstream end of said flexible tubular member abutting and being supported by said annular support;   an annular valve seat at a downstream end of said flexible tubular member;   said valve seat including in conical surface contacting said downstream end of said flexible tubular member; and   and means for forcibly urging said conical surface in an axial direction against said downstream end of said flexible tubular member, whereby said downstream end of said flexible tubular member is deformed into its constricting position in said central passage.   
     
     
       4. A choke valve according to claim 3, wherein said means for forcibly urging includes at least one cylinder having a driving rod movable in response to admission of a pressurized fluid into said cylinder, and means for connecting motion produced by said at least one cylinder and driving rod to said valve seat. 
     
     
       5. A choke valve according to claim 4 wherein: said at least one cylinder includes at least four cylinders angularly spaced about an axis of said choke valve; and   said valve seat includes radially extending members aligned for urging by said at least four cylinders.   
     
     
       6. A choke valve according to claim 1 wherein: said means for deforming includes a plurality of annular passages surrounding said flexible tubular element;   each of said annular passages being independently capable of receiving a pressurized fluid, whereby an adjacent portion of said central passage is deformed into said controllable position; and   said means for successively deforming includes means for successively pressurizing said annular passages, beginning with downstream ones thereof and progressively pressurizing ones upstream, whereby abrasion of said flexible tubular element at deformed portions thereof is accommodated.   
     
     
       7. A choke valve according to claim 6 wherein said means for successively deforming includes progressively depressurizing ones of said annular passages downstream of a furthest-upstream pressurized annular passage, whereby further wear on portions of said flexible tubular element which have previously been abraded is reduced. 
     
     
       8. A choke valve according to claim 1 wherein said flexible tubular element includes a plurality of annular grooves about on inner surface thereof, said plurality of annular grooves providing weak points permitting abraded portions of said flexible tubular element to break off and be carried away with said flow. 
     
     
       9. A choke valve according to claim 8 wherein said flexible tubular element includes a plurality of annular grooves about on outer surface thereof, said plurality of annular grooves providing weak points permitting abraded portions of said flexible tubular element to break off and be carried away with said flow. 
     
     
       10. A choke valve according to claim 1 wherein said flexible tubular element includes a plurality of annular grooves about on outer surface thereof, said plurality of annular grooves providing weak points permitting abraded portions of said flexible tubular element to break off and be carried away with said flow.